1. Field of the Invention
The present invention relates to a plasma etching method of forming a hole by an etching process in a silicon oxide film through a mask, a plasma etching apparatus, a control program, a computer recording medium, and a recording medium having a processing recipe recorded thereon.
2. Description of the Related Art
Conventionally, in a manufacturing process of semiconductor devices, holes such as contact holes have been formed in a silicon oxide film by plasma etching. In such a process of forming the contact holes, so-called bowing is apt to occur in which the shape of the side wall in the hole bulges outward, and therefore it is required to restrain the occurrence of such bowing so as to make the side wall shape almost vertical.
As a plasma etching method of forming the above-described contact hole, two-step etching is known in which main etching is performed using, for example, an etching gas composed of a mixed gas of CHF3/CO/Ar, and then overetching is performed using an etching gas composed of a mixed gas of C4F8/CO/O2/Ar. In other words, in this two-step etching, the main etching is performed using a hydro-fluorocarbon gas under conditions where etching easily proceeds at the bottom of the contact hole but the contact hole is formed in a tapered shape, and thereafter the overetching is performed using a fluorocarbon gas under conditions where etch-stop is apt to occur at the bottom of the contact hole but the contact hole is formed in a vertical shape, thereby keeping the side wall shape of the contact hole vertical as much as possible (see, for example, Japanese Patent Laid-open Application No. 2000-150413)
As a plasma etching method of forming contact holes, for example, two-step etching is also known in which main etching is performed using an etching gas composed of a mixed gas of C4F8/Ar/O2/(CH2F2 or CHF3), and then overetching is performed using an etching gas composed of a mixed gas of C4F8/Ar/CO (see, for example, Japanese Patent Application Laid-open No. 2002-141336).
With miniaturization of semiconductor devices, the diameter of the contact hole and the like are apt to become smaller, and its aspect ration is apt to increase. Specifically, it is required to form a hole with a hole diameter of, for example, 0.13 μm or smaller and an aspect ratio of, for example, 15 or higher. Therefore, with the above-described conventional methods, it has been difficult to form a hole with a fine diameter and a high aspect ratio in an excellent shape, because of occurrence of phenomena such as occurrence of etch-stop, increase in bowing, or the like.